Anti- COVID-19 drug discovery by flavonoid derivatives: an extensive computational drug design approach.

The present study deals with the in-silico analyses of several flavonoid derivatives to explore COVID-19 through pharmacophore modelling, molecular docking, molecular dynamics, drug-likeness, and ADME properties. The initial literature study revealed that many flavonoids, including luteolin, quercetin, kaempferol, and baicalin may be useful against SARS ß-coronaviruses, prompting the selection of their potential derivatives to investigate their abilities as inhibitors of COVID-19. The findings were streamlined using in silico molecular docking, which revealed promising energy-binding interactions between all flavonoid derivatives and the targeted protein. Notably, compounds 8, 9, 13, and 15 demonstrated higher potency against the coronavirus Mpro protein (PDB ID 6M2N). Compound 8 has a -7.2 Kcal/mol affinity for the protein and binds to it by hydrogen bonding with Gln192 and π-sulfur bonding with Met-165. Compound 9 exhibited a significant interaction with the main protease, demonstrating an affinity of -7.9 kcal/mol. Gln-192, Glu-189, Pro-168, and His-41 were the principle amino acid residues involved in this interaction. The docking score for compound 13 is -7.5 Kcal/mol, and it binds to the protease enzyme by making interactions with Leu-41, π-sigma, and Gln-189. These interactions include hydrogen bonding and π-sulfur. The major protease and compound 15 were found to bind with a favourable affinity of -6.8 Kcal/mol. This finding was further validated through molecular dynamic simulation for 1ns, analysing parameters such as RMSD, RMSF, and RoG profiles. The RoG values for all four of the compounds varied significantly (35.2-36.4). The results demonstrated the stability of the selected compounds during the simulation. After passing the stability testing, the compounds underwent screening for ADME and drug-likeness properties, fulfilling all the necessary criteria. The findings of the study may support further efforts for the discovery and development of safe drugs to treat COVID-19.

Structural and virologic mechanism of the emergence of resistance to Mpro inhibitors in SARS-CoV-2.

We generated SARS-CoV-2 variants resistant to three SARS-CoV-2 main protease (Mpro) inhibitors (nirmatrelvir, TKB245, and 5h), by propagating the ancestral SARS-CoV-2WK521WT in VeroE6TMPRSS2 cells with increasing concentrations of each inhibitor and examined their structural and virologic profiles. A predominant E166V-carrying variant (SARS-CoV-2WK521E166V), which emerged when passaged with nirmatrelvir and TKB245, proved to be resistant to the two inhibitors. A recombinant SARS-CoV-2E166V was resistant to nirmatrelvir and TKB245, but sensitive to 5h. X-ray structural study showed that the dimerization of Mpro was severely hindered by E166V substitution due to the disruption of the presumed dimerization-initiating Ser1'-Glu166 interactions. TKB245 stayed bound to MproE166V, whereas nirmatrelvir failed. Native mass spectrometry confirmed that nirmatrelvir and TKB245 promoted the dimerization of Mpro, and compromised the enzymatic activity; the Ki values of recombinant MproE166V for nirmatrelvir and TKB245 were 117±3 and 17.1±1.9 µM, respectively, indicating that TKB245 has a greater (by a factor of 6.8) binding affinity to MproE166V than nirmatrelvir. SARS-CoV-2WK521WT selected with 5h acquired A191T substitution in Mpro (SARS-CoV-2WK521A191T) and better replicated in the presence of 5h, than SARS-CoV-2WK521WT. However, no significant enzymatic or structural changes in MproA191T were observed. The replicability of SARS-CoV-2WK521E166V proved to be compromised compared to SARS-CoV-2WK521WT but predominated over SARS-CoV-2WK521WT in the presence of nirmatrelvir. The replicability of SARS-CoV-2WK521A191T surpassed that of SARS-CoV-2WK521WT in the absence of 5h, confirming that A191T confers enhanced viral fitness. The present data should shed light on the understanding of the mechanism of SARS-CoV-2's drug resistance acquisition and the development of resistance-repellant COVID-19 therapeutics.

Assay Development and Validation for Innovative Antiviral Development Targeting the N-Terminal Autoprocessing of SARS-CoV-2 Main Protease Precursors.

The SARS-CoV-2 main protease (Mpro) is initially synthesized as part of polyprotein precursors that undergo autoproteolysis to release the free mature Mpro. To investigate the autoprocessing mechanism in transfected mammalian cells, we examined several fusion precursors, with the mature SARS-CoV-2 Mpro along with the flanking amino acids (to keep the native substrate sequences) sandwiched between different tags. Our analyses revealed differential proteolysis kinetics at the N- and C-terminal cleavage sites. Particularly, N-terminal processing is differentially influenced by various upstream fusion tags (GST, sGST, CD63, and Nsp4) and amino acid variations at the N-terminal P1 position, suggesting that precursor catalysis is flexible and subject to complex regulation. Mutating Q to E at the N-terminal P1 position altered both precursor catalysis and the properties of the released Mpro. Interestingly, the wild-type precursors exhibited different enzymatic activities compared to those of the released Mpro, displaying much lower susceptibility to known inhibitors targeting the mature form. These findings suggest the precursors as alternative targets for antiviral development. Accordingly, we developed and validated a high-throughput screening (HTS)-compatible platform for functional screening of compounds targeting either the N-terminal processing of the SARS-CoV-2 Mpro precursor autoprocessing or the released mature Mpro through different mechanisms of action.

An ISG15-Based High-Throughput Screening Assay for Identification and Characterization of SARS-CoV-2 Inhibitors Targeting Papain-like Protease.

Emergence of newer variants of SARS-CoV-2 underscores the need for effective antivirals to complement the vaccination program in managing COVID-19. The multi-functional papain-like protease (PLpro) of SARS-CoV-2 is an essential viral protein that not only regulates the viral replication but also modulates the host immune system, making it a promising therapeutic target. To this end, we developed an in vitro interferon stimulating gene 15 (ISG15)-based Förster resonance energy transfer (FRET) assay and screened the National Cancer Institute (NCI) Diversity Set VI compound library, which comprises 1584 small molecules. Subsequently, we assessed the PLpro enzymatic activity in the presence of screened molecules. We identified three potential PLpro inhibitors, namely, NSC338106, 651084, and 679525, with IC50 values in the range from 3.3 to 6.0 µM. These molecules demonstrated in vitro inhibition of the enzyme activity and exhibited antiviral activity against SARS-CoV-2, with EC50 values ranging from 0.4 to 4.6 µM. The molecular docking of all three small molecules to PLpro suggested their specificity towards the enzyme's active site. Overall, our study contributes promising prospects for further developing potential antivirals to combat SARS-CoV-2 infection.

Development of a sensitive high-throughput enzymatic assay capable of measuring sub-nanomolar inhibitors of SARS-CoV2 Mpro.

The SARS-CoV-2 main protease (Mpro) is essential for viral replication because it is responsible for the processing of most of the non-structural proteins encoded by the virus. Inhibition of Mpro prevents viral replication and therefore constitutes an attractive antiviral strategy. We set out to develop a high-throughput Mpro enzymatic activity assay using fluorescently labeled peptide substrates. A library of fluorogenic substrates of various lengths, sequences and dye/quencher positions was prepared and tested against full length SARS-CoV-2 Mpro enzyme for optimal activity. The addition of buffers containing strongly hydrated kosmotropic anion salts, such as citrate, from the Hofmeister series significantly boosted the enzyme activity and enhanced the assay detection limit, enabling the ranking of sub-nanomolar inhibitors without relying on the low-throughput Morrison equation method. By comparing cooperativity in citrate or non-citrate buffer while titrating the Mpro enzyme concentration, we found full positive cooperativity of Mpro with citrate buffer at less than one nanomolar (nM), but at a much higher enzyme concentration (∼320 nM) with non-citrate buffer. In addition, using a tight binding Mpro inhibitor, we confirmed there was only one active catalytical site in each Mpro monomer. Since cooperativity requires at least two binding sites, we hypothesized that citrate facilitates dimerization of Mpro at sub-nanomolar concentration as one of the mechanisms enhances Mpro catalytic efficiency. This assay has been used in high-throughput screening and structure activity relationship (SAR) studies to support medicinal chemistry efforts. IC50 values determined in this assay correlates well with EC50 values generated by a SARS-CoV-2 antiviral assay after adjusted for cell penetration.

New combined Inverse-QSAR and molecular docking method for scaffold-based drug discovery.

Computer-aided drug discovery plays a vital role in developing novel medications for various diseases. The COVID-19 pandemic has heightened the need for innovative approaches to design lead compounds with the potential to become effective drugs. Specifically, designing promising inhibitors of the SARS-CoV-2 main protease (Mpro) is crucial, as it plays a key role in viral replication. Phytochemicals, primarily flavonoids and flavonols from medicinal plants, were screened. Fifty small molecules were selected for molecular docking analysis against SARS-CoV-2 Mpro (PDB ID: 6LU7). Binding energies and interactions were analyzed and compared to those of the anti-SARS-CoV-2 inhibitor Nirmatrelvir. Using these 50 structures as a training set, a QSAR model was built employing simple, reversible topological descriptors. An inverse-QSAR analysis was then performed on 29 = 512 hydroxyl combinations at nine possible positions on the flavone and flavonol scaffold. The model predicted three novel, promising compounds exhibiting the most favorable binding energies (-8.5 kcal/mol) among the 512 possible hydroxyl combinations: 3,6,7,2',4'-pentahydroxyflavone (PF9), 6,7,2',4'-tetrahydroxyflavone (PF11), and 3,6,7,4'-tetrahydroxyflavone (PF15). Molecular dynamics (MD) simulations demonstrated the stability of the PF9/Mpro complex over 300 ns of simulation. These predicted structures, reported here for the first time, warrant synthesis and further evaluation of their biological activity through in vitro and in vivo studies.

Generative artificial intelligence performs rudimentary structural biology modeling.

Natural language-based generative artificial intelligence (AI) has become increasingly prevalent in scientific research. Intriguingly, capabilities of generative pre-trained transformer (GPT) language models beyond the scope of natural language tasks have recently been identified. Here we explored how GPT-4 might be able to perform rudimentary structural biology modeling. We prompted GPT-4 to model 3D structures for the 20 standard amino acids and an α-helical polypeptide chain, with the latter incorporating Wolfram mathematical computation. We also used GPT-4 to perform structural interaction analysis between the anti-viral nirmatrelvir and its target, the SARS-CoV-2 main protease. Geometric parameters of the generated structures typically approximated close to experimental references. However, modeling was sporadically error-prone and molecular complexity was not well tolerated. Interaction analysis further revealed the ability of GPT-4 to identify specific amino acid residues involved in ligand binding along with corresponding bond distances. Despite current limitations, we show the current capacity of natural language generative AI to perform basic structural biology modeling and interaction analysis with atomic-scale accuracy.

Disrupting protease and deubiquitinase activities of SARS-CoV-2 papain-like protease by natural and synthetic products discovered through multiple computational and biochemical approaches.

The single-stranded RNA genome of SARS-CoV-2 encodes several structural and non-structural proteins, among which the papain-like protease (PLpro) is crucial for viral replication and immune evasion and has emerged as a promising therapeutic target. The current study aims to discover new inhibitors of PLpro that can simultaneously disrupt its protease and deubiquitinase activities. Using multiple computational approaches, six compounds (CP1-CP6) were selected from our in-house compounds database, with higher docking scores (-7.97 kcal/mol to -8.14 kcal/mol) and fitted well in the active pocket of PLpro. Furthermore, utilizing microscale molecular dynamics simulations (MD), the dynamic behavior of selected compounds was studied. Those molecules strongly binds at the PLpro active site and forms stable complexes. The dynamic motions suggest that the binding of CP1-CP6 brought the protein to a closed conformational state, thereby altering its normal function. In an in vitro evaluation, CP2 showed the most significant inhibitory potential for PLpro (protease activity = 2.71 ± 0.33 µM and deubiquitinase activity = 3.11 ± 0.75 µM), followed by CP1, CP5, CP4 and CP6. Additionally, CP1-CP6 showed no cytotoxicity at a concentration of 30 µM in the human BJ cell line.

Dual SARS-CoV-2 and MERS-CoV inhibitors from Artemisia monosperma: isolation, structure elucidation, molecular modelling studies, and in vitro activities.

The COVID-19 pandemic has spread throughout the whole globe, so it is imperative that all available resources be used to treat this scourge. In reality, the development of new pharmaceuticals has mostly benefited from natural products. The widespread medicinal usage of species in the Asteraceae family is extensively researched. In this study, compounds isolated from methanolic extract of Artemisia monosperma Delile, a wild plant whose grows in Egypt's Sinai Peninsula. Three compounds, stigmasterol 3-O-ß-D-glucopyranoside 1, rhamnetin 3, and padmatin 6, were first isolated from this species. In addition, five previously reported compounds, arcapillin 2, jaceosidin 4, hispidulin 5, 7-O-methyleriodictyol 7, and eupatilin 8, were isolated. Applying molecular modelling simulations revealed two compounds, arcapillin 2 and rhamnetin 3 with the best docking interactions and energies within SARS-CoV-2 Mpro-binding site (-6.16, and -6.70 kcal mol-1, respectively). The top-docked compounds (2-3) were further evaluated for inhibitory concentrations (IC50), and half-maximal cytotoxicity (CC50) of both SARS-CoV-2 and MERS-CoV. Interestingly, arcapillin showed high antiviral activity towards SARS-CoV-2 and MERS-CoV, with IC50 values of 190.8 µg mL-1 and 16.58 µg mL-1, respectively. These findings may hold promise for further preclinical and clinical research, particularly on arcapillin itself or in collaboration with other drugs for COVID-19 treatment.

Profiling of coronaviral Mpro and enteroviral 3Cpro specificity provides a framework for the development of broad-spectrum antiviral compounds.

The main protease from coronaviruses and the 3C protease from enteroviruses play a crucial role in processing viral polyproteins, making them attractive targets for the development of antiviral agents. In this study, we employed a combinatorial chemistry approach-HyCoSuL-to compare the substrate specificity profiles of the main and 3C proteases from alphacoronaviruses, betacoronaviruses, and enteroviruses. The obtained data demonstrate that coronavirus Mpros exhibit overlapping substrate specificity in all binding pockets, whereas the 3Cpro from enterovirus displays slightly different preferences toward natural and unnatural amino acids at the P4-P2 positions. However, chemical tools such as substrates, inhibitors, and activity-based probes developed for SARS-CoV-2 Mpro can be successfully applied to investigate the activity of the Mpro from other coronaviruses as well as the 3Cpro from enteroviruses. Our study provides a structural framework for the development of broad-spectrum antiviral compounds.

On the dual role of (+)-catechin as primary antioxidant and inhibitor of viral proteases.

Natural antioxidants have become the subject of many investigations due to the role that they play in the reduction of oxidative stress. Their main scavenging mechanisms concern the direct inactivation of free radicals and the coordination of metal ions involved in Fenton-like reactions. Recently, increasing attention has been paid to non-covalent inhibition of enzymes involved in different diseases by the antioxidants. Here, a computational investigation on the primary antioxidant power of (+)-catechin against the •OOH radical has been performed in both lipid-like and aqueous environments, taking into account the relevant species present in the simulated acid-base equilibria at the physiological pH. Hydrogen Atom Transfer (HAT), Single Electron Transfer (SET), and Radical Adduct Formation (RAF) mechanisms were studied, and relative rate constants were estimated. The potential inhibitory activity of the (+)-catechin towards the most important proteases from SARS-CoV-2, 3C-like (Mpro) and papain-like (PLpro) proteases was also investigated by MD simulations to provide deeper atomistic insights on the binding sites. Based on the antioxidant and antiviral properties also unravelled by comparison with other molecules having similar chemical scaffold, our results propose that (+)-CTc satisfies can explicate a dual action as antioxidant and antiviral in particular versus Mpro from SARS-CoV-2.

Dimeric and monomeric conformation of SARS-CoV-2 main protease: New technical approaches based on IR radiation.

The main proteases Mpro are a group of highly conserved cysteine hydrolases in ß-coronaviruses. They have been demonstrated to play an unavoidable role in viral replication, and consequently they have been suggested as key targets for treating coronavirus-caused infectious diseases, mainly from the COVID-19 epidemic. Since the most functional form for Mpro enzymatic activity is associated to its homodimer, compounds inhibiting dimerization should also inhibit catalytic activity. We show how PIR-SEIRA (Plasmonic Internal Reflection-Surface Enhanced InfraRed Absorption) spectroscopy can be a noteworthy technique to study proteins subtle structural variations associated to inhibitor binding. Nanoantennas arrays can selectively confine and enhance electromagnetic field via localized plasmonic resonances, thus promoting ultrasensitive detection of biomolecules in close proximity of nanoantenna arrays and enabling the effective investigation of protein monolayers. By adopting this approach, reflection measurements conducted under back illumination of nanoantennas allow to probe anchored protein monolayers, with minimum contribution of environmental buffer molecules. PIR-SEIRA spectroscopy on Mpro was carried out by ad hoc designed devices, resonating in the spectral region of Amide I and Amide II bands. We evaluated here the structure of anchored monomers and dimers in different buffered environment and in presence of a newly designed Mpro inhibitor. Experimental results show that dimerization is not associated to relevant backbone rearrangements of the protein at secondary structure level, and even if the compound inhibits the dimerization, it is not effective at breaking preformed dimers.

Mutational profiling of SARS-CoV-2 papain-like protease reveals requirements for function, structure, and drug escape.

Papain-like protease (PLpro) is an attractive drug target for SARS-CoV-2 because it is essential for viral replication, cleaving viral poly-proteins pp1a and pp1ab, and has de-ubiquitylation and de-ISGylation activities, affecting innate immune responses. We employ Deep Mutational Scanning to evaluate the mutational effects on PLpro enzymatic activity and protein stability in mammalian cells. We confirm features of the active site and identify mutations in neighboring residues that alter activity. We characterize residues responsible for substrate binding and demonstrate that although residues in the blocking loop are remarkably tolerant to mutation, blocking loop flexibility is important for function. We additionally find a connected network of mutations affecting activity that extends far from the active site. We leverage our library to identify drug-escape variants to a common PLpro inhibitor scaffold and predict that plasticity in both the S4 pocket and blocking loop sequence should be considered during the drug design process.

Disulfiram inhibits coronaviral main protease by conjugating to its substrate entry site.

Coronaviruses (CoV) are highly pathogenic single-strand RNA viruses. CoV infections cause fatal respiratory symptoms and lung injuries in humans and significant economic losses in livestock. Since the SARS-2 outbreak in 2019, the highly conserved main protease (Mpro), also termed 3-chymotrypsin-like protease (3CLpro), has been considered an attractive drug target for treating CoV infections. Mpro mediates the proteolytic cleavage of eleven sites in viral polypeptides necessary for virus replication. Here, we report that disulfiram, an FDA-approved drug for alcoholic treatment, exhibits a broad-spectrum inhibitory effect on CoV Mpros. Analytical ultracentrifugation and circular dichroism analyses indicated that disulfiram treatment blocks the dimeric formation of SARS and PEDV Mpros and decreases the thermostability of SARS, SARS-2, and PEDV Mpros, whereas it facilitates the dimerization and stability of MERS Mpro. Furthermore, mass spectrometry and structural alignment revealed that disulfiram targets the Cys44 residue of Mpros, which is located at the substrate entrance and close to the catalytic His41. In addition, molecular docking analysis suggests that disulfiram conjugation interferes with substrate entry to the catalytic center. In agreement, mutation of Cys44 modulates the disulfiram sensitivity of CoV Mpros. Our study suggests a broad-spectrum inhibitory function of disulfiram against CoV Mpros.

Crystal structures of coronaviral main proteases in complex with the non-covalent inhibitor X77.

Main proteases (Mpros) are a class of conserved cysteine hydrolases among coronaviruses and play a crucial role in viral replication. Therefore, Mpros are ideal targets for the development of pan-coronavirus drugs. X77, previously developed against SARS-CoV Mpro, was repurposed as a non-covalent tight binder inhibitor against SARS-CoV-2 Mpro during COVID-19 pandemic. Many novel inhibitors with favorable efficacy have been discovered using X77 as a reference, suggesting that X77 could be a valuable scaffold for drug design. However, the broad-spectrum performance of X77 and underlying mechanism remain less understood. Here, we reported the crystal structures of Mpros from SARS-CoV-2, SARS-CoV, and MERS-CoV, and several Mpro mutants from SARS-CoV-2 variants bound to X77. A detailed analysis of these structures revealed key structural determinants essential for interaction and elucidated the binding modes of X77 with different coronaviral Mpros. The potencies of X77 against these investigated Mpros were further evaluated through molecular dynamic simulation and binding free energy calculation. These data provide molecular insights into broad-spectrum inhibition against coronaviral Mpros by X77 and the similarities and differences of X77 when bound to various Mpros, which will promote X77-based design of novel antivirals with broad-spectrum efficacy against different coronaviruses and SARS-CoV-2 variants.

3-chymotrypsin-like protease in SARS-CoV-2.

Coronaviruses constitute a significant threat to the human population. Severe acute respiratory syndrome coronavirus-2, SARS-CoV-2, is a highly pathogenic human coronavirus that has caused the coronavirus disease 2019 (COVID-19) pandemic. It has led to a global viral outbreak with an exceptional spread and a high death toll, highlighting the need for effective antiviral strategies. 3-Chymotrypsin-like protease (3CLpro), the main protease in SARS-CoV-2, plays an indispensable role in the SARS-CoV-2 viral life cycle by cleaving the viral polyprotein to produce 11 individual non-structural proteins necessary for viral replication. 3CLpro is one of two proteases that function to produce new viral particles. It is a highly conserved cysteine protease with identical structural folds in all known human coronaviruses. Inhibitors binding with high affinity to 3CLpro will prevent the cleavage of viral polyproteins, thus impeding viral replication. Multiple strategies have been implemented to screen for inhibitors against 3CLpro, including peptide-like and small molecule inhibitors that covalently and non-covalently bind the active site, respectively. In addition, allosteric sites of 3CLpro have been identified to screen for small molecules that could make non-competitive inhibitors of 3CLpro. In essence, this review serves as a comprehensive guide to understanding the structural intricacies and functional dynamics of 3CLpro, emphasizing key findings that elucidate its role as the main protease of SARS-CoV-2. Notably, the review is a critical resource in recognizing the advancements in identifying and developing 3CLpro inhibitors as effective antiviral strategies against COVID-19, some of which are already approved for clinical use in COVID-19 patients.

Cryo2RT: a high-throughput method for room-temperature macromolecular crystallography from cryo-cooled crystals.

Advances in structural biology have relied heavily on synchrotron cryo-crystallography and cryogenic electron microscopy to elucidate biological processes and for drug discovery. However, disparities between cryogenic and room-temperature (RT) crystal structures pose challenges. Here, Cryo2RT, a high-throughput RT data-collection method from cryo-cooled crystals that leverages the cryo-crystallography workflow, is introduced. Tested on endothiapepsin crystals with four soaked fragments, thaumatin and SARS-CoV-2 3CLpro, Cryo2RT reveals unique ligand-binding poses, offers a comparable throughput to cryo-crystallography and eases the exploration of structural dynamics at various temperatures.

Ensemble docking based virtual screening of SARS-CoV-2 main protease inhibitors.

During the first years of COVID-19 pandemic, X-ray structures of the coronavirus drug targets were acquired at an unprecedented rate, giving hundreds of PDB depositions in less than a year. The main protease (Mpro) of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) is the primary validated target of direct-acting antivirals. The selection of the optimal ensemble of structures of Mpro for the docking-driven virtual screening campaign was thus non-trivial and required a systematic and automated approach. Here we report a semi-automated active site RMSD based procedure of ensemble selection from the SARS-CoV-2 Mpro crystallographic data and virtual screening of its inhibitors. The procedure was compared with other approaches to ensemble selection and validated with the help of hand-picked and peer-reviewed activity-annotated libraries. Prospective virtual screening of non-covalent Mpro inhibitors resulted in a new chemotype of thienopyrimidinone derivatives with experimentally confirmed enzyme inhibition.

A SAR and QSAR study on 3CLpro inhibitors of SARS-CoV-2 using machine learning methods.

The 3C-like Proteinase (3CLpro) of novel coronaviruses is intricately linked to viral replication, making it a crucial target for antiviral agents. In this study, we employed two fingerprint descriptors (ECFP_4 and MACCS) to comprehensively characterize 889 compounds in our dataset. We constructed 24 classification models using machine learning algorithms, including Support Vector Machine (SVM), Random Forest (RF), extreme Gradient Boosting (XGBoost), and Deep Neural Networks (DNN). Among these models, the DNN- and ECFP_4-based Model 1D_2 achieved the most promising results, with a remarkable Matthews correlation coefficient (MCC) value of 0.796 in the 5-fold cross-validation and 0.722 on the test set. The application domains of the models were analysed using dSTD-PRO calculations. The collected 889 compounds were clustered by K-means algorithm, and the relationships between structural fragments and inhibitory activities of the highly active compounds were analysed for the 10 obtained subsets. In addition, based on 464 3CLpro inhibitors, 27 QSAR models were constructed using three machine learning algorithms with a minimum root mean square error (RMSE) of 0.509 on the test set. The applicability domains of the models and the structure-activity relationships responded from the descriptors were also analysed.

In Silico Comparative Analysis of Ivermectin and Nirmatrelvir Inhibitors Interacting with the SARS-CoV-2 Main Protease.

Exploring therapeutic options is crucial in the ongoing COVID-19 pandemic caused by SARS-CoV-2. Nirmatrelvir, which is a potent inhibitor that targets the SARS-CoV-2 Mpro, shows promise as an antiviral treatment. Additionally, Ivermectin, which is a broad-spectrum antiparasitic drug, has demonstrated effectiveness against the virus in laboratory settings. However, its clinical implications are still debated. Using computational methods, such as molecular docking and 100 ns molecular dynamics simulations, we investigated how Nirmatrelvir and Ivermectin interacted with SARS-CoV-2 Mpro(A). Calculations using density functional theory were instrumental in elucidating the behavior of isolated molecules, primarily by analyzing the frontier molecular orbitals. Our analysis revealed distinct binding patterns: Nirmatrelvir formed strong interactions with amino acids, like MET49, MET165, HIS41, HIS163, HIS164, PHE140, CYS145, GLU166, and ASN142, showing stable binding, with a root-mean-square deviation (RMSD) of around 2.0 Å. On the other hand, Ivermectin interacted with THR237, THR239, LEU271, LEU272, and LEU287, displaying an RMSD of 1.87 Å, indicating enduring interactions. Both ligands stabilized Mpro(A), with Ivermectin showing stability and persistent interactions despite forming fewer hydrogen bonds. These findings offer detailed insights into how Nirmatrelvir and Ivermectin bind to the SARS-CoV-2 main protease, providing valuable information for potential therapeutic strategies against COVID-19.